Wastewater Treatment Method and Wastewater Treatment System

Abstract

This wastewater treatment system is constituted by being provided with a solid-liquid separator 2 that separates the liquid portion and the solid portion from organic wastewater, a first anaerobic treatment tank 4 that carries out anaerobic treatment of the liquid portion separated by the solid-liquid separator 2 and obtains processed water that has passed through a filter mechanism 3 from sludge, a second anaerobic treatment tank 5 that carries out anaerobic treatment of the solid portion separated by the solid-liquid separator 2 , and a sludge supply mechanism 6 that supplies the sludge in the second anaerobic treatment tank 5 to the first anaerobic treatment tank 4 , and the filter mechanism functions stably without increasing the size of the anaerobic treatment tanks.

1 - 16 . (canceled) 
     
     
         17 . A wastewater treatment method of carrying out biological treatment of organic wastewater under an anaerobic condition,
 the method comprising:   a solid-liquid separation step of separating a liquid portion and a solid portion from the organic wastewater;   a first anaerobic treatment step of carrying out anaerobic treatment of the liquid portion separated in the solid-liquid separation step and obtaining treated water, that has passed through a filter mechanism, from sludge in the anaerobic treatment;   a second anaerobic treatment step of carrying out anaerobic treatment of the solid portion separated in the solid-liquid separation step; and   a sludge supply step of supplying the sludge treated in the second anaerobic treatment step to the first anaerobic treatment step.   
     
     
         18 . The wastewater treatment method according to  claim 17 ,
 wherein the filter mechanism used in the first anaerobic treatment step is a membrane separator.   
     
     
         19 . The wastewater treatment method according to  claim 18 ,
 wherein the first anaerobic treatment step includes an air diffusion step of diffusing biogas, produced in the anaerobic treatment, from below the membrane separator immersed and disposed in the sludge.   
     
     
         20 . The wastewater treatment method according to  claim 17 ,
 wherein the second anaerobic treatment step is carried out in a warmed state in which the sludge is warmed.   
     
     
         21 . The wastewater treatment method according to  claim 17 ,
 wherein the second anaerobic treatment step is carried out in the warmed state in which the sludge is warmed by using biogas, produced in the second anaerobic treatment step, as fuel.   
     
     
         22 . The wastewater treatment method according to  claim 17 , further comprising:
 a recovery step of recovering biogas, dissolved in the treated water that has passed through the filter mechanism, by aeration treatment or decompression treatment.   
     
     
         23 . The wastewater treatment method according to  claim 17 , further comprising:
 a nitrification step of turning ammonia, dissolved in the treated water that has passed through the filter mechanism, into nitric acid;   a denitrification step of denitrifying the nitric acid produced in the nitrification step; and   a solid-liquid separation step of separating sludge from treated water that has gone through the denitrification step.   
     
     
         24 . A wastewater treatment method of carrying out biological treatment of organic wastewater under an anaerobic condition, the method comprising:
 a solid-liquid separation step of separating a liquid portion and a solid portion from the organic wastewater;   a first anaerobic treatment step of carrying out anaerobic treatment of the liquid portion separated in the solid-liquid separation step and obtaining treated water, that has passed through a filter mechanism, from sludge in the anaerobic treatment;   a second anaerobic treatment step of carrying out anaerobic treatment of the solid portion separated in the solid-liquid separation step and having a longer sludge retention time than the first anaerobic treatment step; and   a sludge supply step of supplying the sludge treated in the second anaerobic treatment step to the first anaerobic treatment step.   
     
     
         25 . The wastewater treatment method according to  claim 24 ,
 wherein the sludge retention time in the second anaerobic treatment step is set to 15 to 30 days and the sludge retention time in the first anaerobic treatment step is set to be shorter than 15 days.   
     
     
         26 . The wastewater treatment method according to  claim 24 ,
 wherein the filter mechanism used in the first anaerobic treatment step is a membrane separator.   
     
     
         27 . The wastewater treatment method according to  claim 26 ,
 wherein the first anaerobic treatment step includes an air diffusion step of diffusing biogas, produced in the anaerobic treatment, from below the membrane separator immersed and disposed in the sludge.   
     
     
         28 . The wastewater treatment method according to  claim 24 ,
 wherein the second anaerobic treatment step is carried out in the warmed state in which the sludge is warmed by using biogas, produced in the second anaerobic treatment step, as fuel.   
     
     
         29 . The wastewater treatment method according to  claim 24 , further comprising:
 a recovery step of recovering biogas, dissolved in the treated water that has passed through the filter mechanism, by aeration treatment or decompression treatment.   
     
     
         30 . The wastewater treatment method according to  claim 24 , further comprising:
 a nitrification step of turning ammonia, dissolved in the treated water that has passed through the filter mechanism, into nitric acid;   a denitrification step of denitrifying the nitric acid produced in the nitrification step; and   a solid-liquid separation step of separating sludge from treated water that has gone through the denitrification step.   
     
     
         31 . A wastewater treatment system of carrying out biological treatment of organic wastewater under an anaerobic condition,
 the system comprising:   a solid-liquid separator configured to separate a liquid portion and a solid portion from the organic wastewater;   a first anaerobic treatment tank configured to carry out anaerobic treatment of the liquid portion separated in the solid-liquid separator and obtaining treated water, that has passed through a filter mechanism, from sludge in the anaerobic treatment;   a second anaerobic tank configured to carry out anaerobic treatment of the solid portion separated in the solid-liquid separator; and   a sludge supply mechanism configured to supply the sludge in the second anaerobic treatment tank to the first anaerobic treatment tank.   
     
     
         32 . The wastewater treatment system according to  claim 31 ,
 wherein the filter mechanism provided to the first anaerobic treatment tank is a membrane separator.   
     
     
         33 . The wastewater treatment system according to  claim 31 ,
 wherein the filter mechanism includes   a membrane separator immersed and disposed in the sludge in the first anaerobic treatment tank, and   an air diffuser disposed below the membrane separator to diffuse biogas produced in the anaerobic treatment.   
     
     
         34 . The wastewater treatment system according to  claim 31 ,
 wherein the filter mechanism is a member that is selected from a mesh filter, a screen, a ceramic porous body, and a sponge porous body and that prevents passage of a particle having a particle diameter of 1 μm or less.   
     
     
         35 . The wastewater treatment system according to  claim 31 , wherein the second anaerobic treatment tank includes a warming mechanism configured to warm the sludge in the tank. 
     
     
         36 . The wastewater treatment system according to  claim 31 , further comprising:
 a nitrification tank configured to turn ammonia, dissolved in the treated water that has been separated by the filter mechanism, into nitric acid;   an anoxic tank configured to denitrify the nitric acid produced in the nitrification tank; and   a solid-liquid separator configured to separate sludge from treated water that has passed through the anoxic tank.